Road dust emissions from unpaved surfaces: guide to reporting

This document provides guidance on how you can calculate the particulate matter (PM) emissions from vehicles travelling on unpaved roads to report to the National Pollutant Release Inventory (NPRI).      

This updated guidance replaces all previous versions.

The NPRI has also developed a spreadsheet calculator to help you estimate the PM generated by vehicles travelling on unpaved roads at your facility.  Note: Use this calculator to estimate emissions from one road segment at a time. You must calculate emissions from each road segment at your facility and then add them together. This number will be the final release estimate for your facility.

Background

There are three particulate matter fractions you must consider when estimating road dust emissions:

• total particulate matter (TPM)
• particulate matter less than or equal to 10 microns in diameter (PM₁₀)
• particulate matter less than or equal to 2.5 microns in diameter (PM_2.5)

The reporting threshold

The reporting of road dust emissions from unpaved surfaces may be required from your facility if the following conditions are met:

• the employee threshold was met (20,000 employee hours), or
• there are specified activities to which the employee threshold does not apply take place

AND

• vehicles travelled more than 10,000 km on unpaved road surfaces within the facility

If your facility meets the above criteria, you must complete the following steps for each size of PM:

1. Estimate the emissions of the PM fraction from unpaved road surfaces.
2. Combine the emissions of the PM from road dust with releases from all other sources of the PM at the facility.
3. Compare the quantity of the PM from all sources at the facility to the reporting threshold (refer to Table 1).
4. Report releases of the PM fraction (including dust from unpaved roads) if the reporting threshold for the PM fraction is met or exceeded.

An unpaved road

Common types of unpaved road surfaces include:

• gravel road surfaces
• thin membrane bituminous surfaces
• surface treatments
• bituminous cold mix surfaces

If a dust suppressant is applied to an unpaved road, this segment of road is still considered to be an unpaved road surface. A paved road is defined as any road that has a semi-permanent surface placed on it (for example, asphalt or concrete).

Calculating emissions of road dust from unpaved road surfaces

You should use the following generalized equation to determine the emissions of each size of PM from unpaved road surfaces (USEPA, 2006):

E_x = VKT*EF_x*ADJ*(1-CE/100)                                                                                    (1)

Where:

• E_x: Emission of contaminant x, kg
• VKT: Annual total vehicle kilometres travelled, km
• EF_x: Emission factor of contaminant x, kg/VKT
• ADJ: Adjustment factor for precipitation, snow cover and frozen days
• CE: Applied Dust Control Method’s efficiency, %

The following sections describe the process you should follow when using equation 1.

Step 1: Determine the annual total vehicle kilometres travelled (VKT)

The VKT represents the kilometres travelled by all vehicles operated at the facility on unpaved roads. This includes all vehicles that come into the facility through some form of controlled access such as a security gate, including any contractor vehicles or vehicles that belong to customers. All other vehicles that enter the site through uncontrolled access (for example, public right-of-way, Crown land access) are not to be included in either the threshold calculation or the final release estimates because your facility has no control over the road dust these vehicles generate.

For the purpose of NPRI reporting, “vehicle” refers to any mobile equipment that is capable of self-propulsion (for example, fleet vehicles and earth-moving equipment, including, but not limited to, loaders, dump trucks, forklifts, excavators and bulldozers).

The annual VKT should be obtained with the best available data. This can be odometer readings, the length of roads within your facility and the number of vehicles coming into your facility on a typical day. If no data are available, surveys can be conducted throughout the year on representative days of operation to estimate the total VKT.

Step 2: Determine the emission factor (EF) to be used

The United States Environmental Protection Agency (USEPA) has developed an empirical equation (equation 2) for vehicles travelling on unpaved road surfaces at industrial sites. The equation takes into account the silt content of the roadway and the mean weight of the vehicles travelling on the road. (For more information, refer to AP 42, Chapter 13: Miscellaneous Sources, Section 2.2, (USEPA, 2006)).

The emission factor in metric units (that is, kilograms/VKT) is calculated using the following equation:

EF = k*(s/12)^a*(W/2.72)^b                                                                                       (2)

Where:

• EF: Size-specific emission factor, kg/VKT
• s: Surface material silt content, %
• W: Mean vehicle weight, tonnes (metric)
• k, a, b:  Numerical constants for calculation (refer to Table 2)

Notes:

• the term (W/2.72) in equation (2) has been modified from the original term (W/3) in the AP-42 equation to allow for metric vehicle weights
• the facility may have unpaved roads that are only travelled by light vehicles. If this is the case, you may use the USEPA’s equation 1b from for public unpaved roads travelled mostly by light-duty vehicles with mean vehicle weights less than 2.7 tonnes (AP 42, Chapter 13: Miscellaneous Sources, Section 13.2.2.2, (USEPA, 2006))

The silt content (that is, “s”) may be obtained using the USEPA test method (Appendix C.1: Procedures for sampling surface/Bulk dust loading, AP-42, USEPA, 2003). However, if you do not have a site-specific value for the silt content, an appropriate mean value from Table AP-42 13.2.2-1 (USEPA, 2006), reproduced below in Table 3, may be used as a default value. However, the use of the default values may affect the quality of estimated values.

It is important to note that the only vehicle-related parameter used in the EF determination is the mean weight of the fleet using the road segment. For example, if 86% of traffic on the road is 300-tonne trucks, while the remaining 14% is 55-tonne trucks, then the mean weight is 265 tonnes (0.86 x 300 + 0.14 x 55). You should use the vehicle mean weight value instead of doing a separate calculation for each vehicle class travelling on a given unpaved road.

Step 3: Calculate the adjustment factor (ADJ) for precipitation, snow cover and frozen days

Road dust emissions are reduced due to the natural mitigation effects of precipitation (rain and snow falls), as well as on frozen or snow-covered roads. Equation 1 assumes that no dust emissions occur on days with precipitation exceeding 0.2 mm or on days when the road surface is covered with snow or is frozen without high traffic volume.

The ADJ value used in equation 1 is determined using the following equation:

ADJ = (Working Days-(p+snow))/Working Days                                             (3)

Where:

• ADJ: Adjustment factor for precipitation, snow cover and frozen days
• Working Days: The number of operating days per year
• p: Estimated Annual Working Days with precipitation exceeding 0.2 mm
• snow: The estimated Annual Working Days when the roads were frozen or snow-covered and wet for winter

With respect to precipitation and snow-covered days, you can use your facility-specific information if it is available. Information about precipitation and snow cover may also be taken from the nearest meteorological station on Environment Canada’s Historical Climate Data website. You can use the Climate Normals Data between 1971 to 2000 or the information from the Monthly Climate Summaries for the reporting year. It is worth noting that the information you retrieve from the Climate Normals Data should be for the days with precipitation exceeding 0.2 mm and the days with snow depth of more than 1 cm.

When calculating ADJ using Environment Canada’s climate data, you must pay attention to the sum of precipitation and snow-cover days and working days. Note: You should ensure that the “p+snow” value for a specific month is not greater than the number of days worked in that month. If it is greater, then you should use the number of days worked instead. For example, if there are 20 working days in December and "p+snow" is 25 days, then you should use 20 days for December in order to calculate the total annual "p+snow." You should also avoid double counting when further total precipitation (sum of the total rainfall and the water equivalent of the total snowfall in mm) accumulates on days where roads are already frozen or snow covered and wet for winter.

Step 4: Determine the impact of dust control methods (CE)

Several techniques are used to reduce road dust emissions caused by vehicular travel on industrial unpaved road surfaces, such as the application of water or chemical dust suppressants (Buonicore and Davis, 1992; USEPA, 1987).

Watering is the most common control technique used for unpaved road surfaces (AMEC, 2007). The control efficiency of watering depends on the application rate, the elapsed time between applications, traffic volume and meteorological conditions.

Chemical stabilization is also used to reduce emissions of road dust from unpaved surfaces. Its control efficiency depends on the material used and the method of application. You should consult with the vendor to obtain the control efficiency for a specific chemical stabilization process used within your facility. However, average performance curves for petroleum resin products used on unpaved road surfaces have been generated. More details can be found in Figure 13.2.2-5, AP-42 chapter 13.2.2 (USEPA, 2006).

Table 4 lists publically available dust control methods and their respective efficiencies.

References

The development of methodology, Activity Data and emission factors for estimating fugitive particulates from the aggregate mining and rock quarrying sector, 2007, AMEC Earth & Environmental, Internal report submitted to Environment Canada, Hamilton, Ontario, Canada

Fugitive Emissions. Air Pollution Engineering Manual, Chapter 4, First Edition, 1992, Buonicore and Davis, AWMA, New York, USA

Particulate Emission Measurements from controlled construction Activities, 2001, EPA/600/R-01/031. Midwest Research Institute, Kansas City, Kansas, USA

Unpaved Roads-Chapter 13.2.2, AP-42, Compilation of Air Pollutant Emission Factors, Volume 1, Stationary Point and Area Sources, 2006, USEPA, USA

Appendix C.1: Procedures for sampling surface/Bulk dust loading, AP-42, Compilation of Air Pollutant Emission Factors, Volume 1, Stationary Point and Area Sources, 2003, USEPA, USA

Emission Control technologies and emission factors for unpaved road fugitive emissions, User’s Guide, 1987, EPA/625/5-87/022, USEPA, USA

Fugitive Dust Control Measures Applicable for the Western Regional Air Partnership’s (WRAP). Fugitive Dust Handbook, 2004, Western Governor’s Association, Denver, Colorado, USA